Thursday, December 13, 2007

California's Hayward Fault

I caught this on the web, didn't see it in my journal yet. They are making a big deal out of this, but all of California is a big mish-mash of faults. The article has a very interesting map, though, and it shows how a lot of faults are interconnected.

In California, they make a big deal out of 'segments' in their faults. They like to feel that if an earthquake has terminated in the past at one point, it will always do so. And if they map a trivial one-mile gap in the fault, then it is significant. Boy, has Nature got a surprise for them!

In reality, this doesn't make much difference for the average bridge, or house. The big threat is always the earthquake right beneath you, and if it comes as a 500 km fault rupture, or a 50 km rupture, it still packs some velocity. As well, being on soft soft in a basin amplifies by about a factor of 100, so they will react to any earthquake. A big earthquake just affects a lot more people all at once, so this has an impact on recovery efforts.

In the end, I can look at a big long active fault, and not know whether the future holds one big, full length rupture, or a lot of in-betweens. As with the upcoming big Vancouver earthquake, it could be a big slip, or a decade of terror!